What draws you to stories like those of Sweeney Todd and Maria Marten?
For me, a good melodrama is half way between opera and music hall. It has the passion of the former and is as much fun as the latter. It needs an exciting story, larger than life characters, music, whirling words, suspense, surprises, and cheap laughs. All delivered hot and strong, and much of it directly to the audience. It would be nice if it was a spectacle too; but in these hard times the more outrageously expensive effects are probably best left to the kind of West End musicals where you come out humming the scenery... I think everything I've ever written has a bit of melodrama in it; I don't do realism in the theatre – it doesn't work for me. Actors and audiences are all in the same room, and to pretend there's a “fourth wall” between them seems daft. So I'm naturally drawn to stories like Sweeney, Dracula and Maria, all of which I've done versions of, as well as adapting novels by Charles Dickens and Victor Hugo. These original sources all predate the cinema, let alone television, and take us back to a time when theatre was the most popular – and populist – form of entertainment; when it played to its strengths and tried to engage audiences' emotions to make 'em laugh, cry, get angry, feel scared – whatever.

How do you think that 21st century audiences differ from previous ones in their attitudes to villains, heroes and so on?

I'm not sure there's that much difference to be honest. William Corder's trial and execution for Maria's murder in 1828 was a tabloid sensation – but it probably generated roughly the same number of column inches as Katy Price and Peter Andre's marital mayhem, let alone Wayne Rooney's ups and downs. And can it be long before we're offered Roo the Moosical!? Maybe in terms of theatre we're marginally more sophisticated in terms of what we expect when we go to see a show (comfy seats, quilted bog paper in the loos) but I hope, as the late, great Ken Campbell maintained, we're still sensation seekers at heart...

Characters in melodramas tend to be black and white; why do you explore shades of grey? And having given Sweeney a motive; how do you approach Corder?

How dare you say my characters are grey?! They're supposed to be scarlet, or purple, or sky blue pink... But post-Freud I think we do demand that our monsters have some psychological justification for their behaviour, even if it's as tenuous as Hannibal Lechter being so clever that he thinks he's God. I made Sweeney Todd into a revenger in the style of 17th century revenge tragedy, but I was faced with a different problem when approaching William Corder. All the evidence suggests that he was a brutal drunk who murdered Maria because she was inconvenient; and Maria herself, far from being an innocent young maid, was an unmarried mother of two kids by different fathers, and also had a drink problem. Not a very inspiring scenario, and not much of a blueprint for passion and fun. So I decided that I would ignore the facts and model my William Corder on Lord Byron; and make him an aristocratic, anti-establishment radical, poet, and serial shagger, who falls head over heels in love for the first time in his life, and commits murder because – well if I tell you that, I'll spoil the show so you'll have to buy your ticket to find out.

What are you working on at the moment?

At present I'm halfway through writing a show with the working title The Banker of Malta, a very loose reworking of Christopher Marlowe's The Jew of Malta which was written in 1590. The original tells the story of a three-way war on the island of Malta, between Jews, Christian & Muslims – sounds familiar? Although in this case it's about money. not oil or land. And surprise, surprise, it's a bit of a melodrama... Whole nunneries poisoned, duels and disguises, and the hero is ultimately boiled in oil. I thought it might be interesting to make the central character a member of everybody's least favourite profession, not that he's any worse than the (Christian) politicians, or the (Muslim) Jihadists. Never mind, hopefully the women will sort it out in the second act...

(The Mysterie of Maria Marten and the Murder in the Red Barn opens at the Queen's Theatre, Hornchurch on 1 November with previews on 29 and 30 October. It runs until 20 November).